/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/****************************************************************************
 * drivers/loop.c
 *
 *   Copyright (C) 2008-2009, 2011, 2014 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/config.h>

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/mount.h>

#include <stdint.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <semaphore.h>
#include <debug.h>
#include <errno.h>

#include <tinyara/kmalloc.h>
#include <tinyara/fs/fs.h>

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

#define loop_semgive(d) sem_post(&(d)->sem)	/* To match loop_semtake */
#define MAX_OPENCNT     (255)	/* Limit of uint8_t */

/****************************************************************************
 * Private Types
 ****************************************************************************/

struct loop_struct_s {
	sem_t sem;					/* For safe read-modify-write operations */
	uint32_t nsectors;			/* Number of sectors on device */
	off_t offset;				/* Offset (in bytes) to the first sector */
	uint16_t sectsize;			/* The size of one sector */
	uint8_t opencnt;			/* Count of open references to the loop device */
#ifdef CONFIG_FS_WRITABLE
	bool writeenabled;			/* true: can write to device */
#endif
	int fd;						/* Descriptor of char device/file */
};

/****************************************************************************
 * Private Function Prototypes
 ****************************************************************************/

static int loop_semtake(FAR struct loop_struct_s *dev);
static int loop_open(FAR struct inode *inode);
static int loop_close(FAR struct inode *inode);
static ssize_t loop_read(FAR struct inode *inode, FAR unsigned char *buffer, size_t start_sector, unsigned int nsectors);
#ifdef CONFIG_FS_WRITABLE
static ssize_t loop_write(FAR struct inode *inode, FAR const unsigned char *buffer, size_t start_sector, unsigned int nsectors);
#endif
static int loop_geometry(FAR struct inode *inode, FAR struct geometry *geometry);

/****************************************************************************
 * Private Data
 ****************************************************************************/

static const struct block_operations g_bops = {
	loop_open,					/* open     */
	loop_close,					/* close    */
	loop_read,					/* read     */
#ifdef CONFIG_FS_WRITABLE
	loop_write,					/* write    */
#else
	NULL,						/* write    */
#endif
	loop_geometry,				/* geometry */
	NULL						/* ioctl    */
};

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: loop_semtake
 ****************************************************************************/

static int loop_semtake(FAR struct loop_struct_s *dev)
{
	int ret;

	/* Take the semaphore (perhaps waiting) */

	ret = sem_wait(&dev->sem);
	if (ret < 0) {
		int errcode = get_errno();

		/* The only case that an error should occur here is if
		 * the wait was awakened by a signal.
		 */

		ASSERT(errcode == EINTR);
		return -ret;
	}

	return OK;
}

/****************************************************************************
 * Name: loop_open
 *
 * Description: Open the block device
 *
 ****************************************************************************/

static int loop_open(FAR struct inode *inode)
{
	FAR struct loop_struct_s *dev;
	int ret;

	DEBUGASSERT(inode && inode->i_private);
	dev = (FAR struct loop_struct_s *)inode->i_private;

	/* Make sure we have exclusive access to the state structure */

	ret = loop_semtake(dev);
	if (ret == OK) {
		if (dev->opencnt == MAX_OPENCNT) {
			ret = -EMFILE;
		} else {
			/* Increment the open count */

			dev->opencnt++;
		}

		loop_semgive(dev);
	}

	return ret;
}

/****************************************************************************
 * Name: loop_close
 *
 * Description: close the block device
 *
 ****************************************************************************/

static int loop_close(FAR struct inode *inode)
{
	FAR struct loop_struct_s *dev;
	int ret;

	DEBUGASSERT(inode && inode->i_private);
	dev = (FAR struct loop_struct_s *)inode->i_private;

	/* Make sure we have exclusive access to the state structure */

	ret = loop_semtake(dev);
	if (ret == OK) {
		if (dev->opencnt == 0) {
			ret = -EIO;
		} else {
			/* Decrement the open count */

			dev->opencnt--;
		}

		loop_semgive(dev);
	}

	return ret;
}

/****************************************************************************
 * Name: loop_read
 *
 * Description:  Read the specified number of sectors
 *
 ****************************************************************************/

static ssize_t loop_read(FAR struct inode *inode, FAR unsigned char *buffer, size_t start_sector, unsigned int nsectors)
{
	FAR struct loop_struct_s *dev;
	ssize_t nbytesread;
	off_t offset;
	int ret;

	DEBUGASSERT(inode && inode->i_private);
	dev = (FAR struct loop_struct_s *)inode->i_private;

	if (start_sector + nsectors > dev->nsectors) {
		dbg("Read past end of file\n");
		return -EIO;
	}

	/* Calculate the offset to read the sectors and seek to the position */

	offset = start_sector * dev->sectsize + dev->offset;
	ret = lseek(dev->fd, offset, SEEK_SET);
	if (ret == (off_t)-1) {
		dbg("Seek failed for offset=%d: %d\n", (int)offset, get_errno());
		return -EIO;
	}

	/* Then read the requested number of sectors from that position */

	do {
		nbytesread = read(dev->fd, buffer, nsectors * dev->sectsize);
		if (nbytesread < 0 && get_errno() != EINTR) {
			dbg("Read failed: %d\n", get_errno());
			return -get_errno();
		}
	} while (nbytesread < 0);

	/* Return the number of sectors read */

	return nbytesread / dev->sectsize;
}

/****************************************************************************
 * Name: loop_write
 *
 * Description: Write the specified number of sectors
 *
 ****************************************************************************/

#ifdef CONFIG_FS_WRITABLE
static ssize_t loop_write(FAR struct inode *inode, FAR const unsigned char *buffer, size_t start_sector, unsigned int nsectors)
{
	FAR struct loop_struct_s *dev;
	ssize_t nbyteswritten;
	off_t offset;
	int ret;

	DEBUGASSERT(inode && inode->i_private);
	dev = (FAR struct loop_struct_s *)inode->i_private;

	/* Calculate the offset to write the sectors and seek to the position */

	offset = start_sector * dev->sectsize + dev->offset;
	ret = lseek(dev->fd, offset, SEEK_SET);
	if (ret == (off_t)-1) {
		dbg("Seek failed for offset=%d: %d\n", (int)offset, get_errno());
	}

	/* Then write the requested number of sectors to that position */

	do {
		nbyteswritten = write(dev->fd, buffer, nsectors * dev->sectsize);
		if (nbyteswritten < 0 && get_errno() != EINTR) {
			dbg("Write failed: %d\n", get_errno());
			return -get_errno();
		}
	} while (nbyteswritten < 0);

	/* Return the number of sectors written */

	return nbyteswritten / dev->sectsize;
}
#endif

/****************************************************************************
 * Name: loop_geometry
 *
 * Description: Return device geometry
 *
 ****************************************************************************/

static int loop_geometry(FAR struct inode *inode, FAR struct geometry *geometry)
{
	FAR struct loop_struct_s *dev;

	DEBUGASSERT(inode);
	if (geometry) {
		dev = (FAR struct loop_struct_s *)inode->i_private;
		geometry->geo_available = true;
		geometry->geo_mediachanged = false;
#ifdef CONFIG_FS_WRITABLE
		geometry->geo_writeenabled = dev->writeenabled;
#else
		geometry->geo_writeenabled = false;
#endif
		geometry->geo_nsectors = dev->nsectors;
		geometry->geo_sectorsize = dev->sectsize;
		return OK;
	}

	return -EINVAL;
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: losetup
 *
 * Description:
 *   Setup the loop device so that it exports the file referenced by 'filename'
 *   as a block device.
 *
 ****************************************************************************/

int losetup(FAR const char *devname, FAR const char *filename, uint16_t sectsize, off_t offset, bool readonly)
{
	FAR struct loop_struct_s *dev;
	struct stat sb;
	int ret;

	/* Sanity check */

#ifdef CONFIG_DEBUG
	if (!devname || !filename || !sectsize) {
		return -EINVAL;
	}
#endif

	/* Get the size of the file */

	ret = stat(filename, &sb);
	if (ret < 0) {
		dbg("Failed to stat %s: %d\n", filename, get_errno());
		return -get_errno();
	}

	/* Check if the file system is big enough for one block */

	if (sb.st_size - offset < sectsize) {
		dbg("File is too small for blocksize\n");
		return -ERANGE;
	}

	/* Allocate a loop device structure */

	dev = (FAR struct loop_struct_s *)kmm_zalloc(sizeof(struct loop_struct_s));
	if (!dev) {
		return -ENOMEM;
	}

	/* Initialize the loop device structure. */

	sem_init(&dev->sem, 0, 1);
	dev->nsectors = (sb.st_size - offset) / sectsize;
	dev->sectsize = sectsize;
	dev->offset = offset;

	/* Open the file. */

#ifdef CONFIG_FS_WRITABLE
	dev->writeenabled = false;	/* Assume failure */
	dev->fd = -1;

	/* First try to open the device R/W access (unless we are asked
	 * to open it readonly).
	 */

	if (!readonly) {
		dev->fd = open(filename, O_RDWR);
	}

	if (dev->fd >= 0) {
		dev->writeenabled = true;	/* Success */
	} else
#endif
	{
		/* If that fails, then try to open the device read-only */

		dev->fd = open(filename, O_RDWR);
		if (dev->fd < 0) {
			dbg("Failed to open %s: %d\n", filename, get_errno());
			ret = -get_errno();
			goto errout_with_dev;
		}
	}

	/* Inode private data will be reference to the loop device structure */

	ret = register_blockdriver(devname, &g_bops, 0, dev);
	if (ret < 0) {
		fdbg("register_blockdriver failed: %d\n", -ret);
		goto errout_with_fd;
	}

	return OK;

errout_with_fd:
	close(dev->fd);
errout_with_dev:
	kmm_free(dev);
	return ret;
}

/****************************************************************************
 * Name: loteardown
 *
 * Description:
 *   Undo the setup performed by losetup
 *
 ****************************************************************************/

int loteardown(FAR const char *devname)
{
	FAR struct loop_struct_s *dev;
	FAR struct inode *inode;
	int ret;

	/* Sanity check */

#ifdef CONFIG_DEBUG
	if (!devname) {
		return -EINVAL;
	}
#endif

	/* Open the block driver associated with devname so that we can get the inode
	 * reference.
	 */

	ret = open_blockdriver(devname, MS_RDONLY, &inode);
	if (ret < 0) {
		dbg("Failed to open %s: %d\n", devname, -ret);
		return ret;
	}

	/* Inode private data is a reference to the loop device structure */

	dev = (FAR struct loop_struct_s *)inode->i_private;
	close_blockdriver(inode);

	DEBUGASSERT(dev);

	/* Are there still open references to the device */

	if (dev->opencnt > 0) {
		return -EBUSY;
	}

	/* Otherwise, unregister the block device */

	ret = unregister_blockdriver(devname);

	/* Release the device structure */

	if (dev->fd >= 0) {
		(void)close(dev->fd);
	}

	kmm_free(dev);
	return ret;
}
